Based On The Mode Parameter, The Damage Of The Truss Is Identified.

Structural health monitoring technology (SHMT) was developed last middle century. At first, SHMT was applied in the field such as the load monitoring of aviation and spaceflight .With the development of the economic and science, modern project structures are proceeding at the direction of maximization and complication. The complicated environments do all kinds of threat to the structures. To guarantee the structures' safety, the damage researches must be done to the structures to get the correct operation conditions, then the accurate repairing work can be done to the damage timely. The specialists and scholars study the health of the civil engineering by SHMT. So it is meaningful to research how to identify the damage of the truss structures.This paper introduced the research background, actuality and the damage identification theory (DIT) of SHMT in China and in the world. The vibration characteristic and DIT based on the modal analysis and numerical simulation of the truss were introduced importantly.The truss structures are used in many large factory buildings and bridges for its light weight and high utilization ratio. It is meaningful to research how to identify the damage of the truss structures. So, the cantilever truss structure was regarded as the research object. It proposes the method of changing displacement of nodes to strain of elements for the special character of the truss rod, and then identify the damage by the changing of the strain modal of undamaged and damaged structure.This paper studied the cantilever truss by numerical simulation. The frequency and strain modal change rule were discussed when the truss have the single. The conclusions were obtained as follow:(1) When the each rod of the cantilever truss produces the same damage degree, the frequency of the truss reduces as the distance is increased between fixation hinge seat and the rod. The frequency of the truss increases as the damage degree increases.(2) In all strain modals, the damage can be identified accurately when the strain value ofthe damaged position is adopted.(3)The result of the damage level is same, the value of relative strain is close to the real damage level when the structure is damaged under 20%, and when it is damaged above 20%, the value of the relative strain exceeds greatly the real damage level.Obtained the frequency change rule by the modal analysis, the results prove that the modal strain is the sensitive parameter for damage identification and it identifies the damage effectively.